PARENT SESSION
Organized Oral Session 18: Ecological guidelines for management of water quantity and quality in agricultural landscapes
Organizer(s): L Ryszkowski and R Lowrance
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal

Ecohydrology of riparian zones in Rhode Island and areas of the glaciated northeastern United States.

Kellogg, Q.^*,1, Addy, Kelly¹, Gold, Arthur¹, Groffman, Peter^{1, 2}, Stolt, Mark¹, ¹ University of Rhode Island, Kingston, RI, USA² Institute of Ecosystem Studies, Millbrook, NY, USA

ABSTRACT- Riparian zones can serve as important zones of denitrification, reducing nitrogen loading to streams and coastal areas. At the field and regional scales, variability in riparian groundwater flow paths and the distribution and the extent of organic soils impedes efforts to assess the potential for riparian transformation of catchment N. We studied in situ groundwater denitrification using geomorphic setting as a hypothetical framework. Glaciated regions such as the northeastern United States are often divided into three major geomorphic settings: glacial till, glacial outwash, and alluvial soils characterized by a recurring pattern of mineral layers and layers of high organic–C content. It is commonly assumed that substantial groundwater denitrification only occurs within the shallow (< 1 m) portion of the soil profile, often referred to as the biologically active zone, and that deep groundwater flow bypasses this portion of the riparian zone. Deep groundwater flow is common in both glacial outwash and alluvial settings. We hypothesized that in outwash settings denitrification rates would drop precipitously with depth, following the expected carbon distribution. In contrast, in alluvial settings where carbon–rich deposits are found deep in the soil profile, denitrification rates would not drop significantly with depth. We used ¹⁵N–enriched nitrate to evaluate in situ denitrification rates down to 3 m in both settings. Rates were not significantly different when sites were grouped by setting. Rates were inversely correlated with distance from the stream, with no decline down to 3 m within 10 m of the stream, regardless of setting. A field study of lower order streams found soils mapped as hydric outwash routinely had buried organic–rich horizons, and their presence was more likely with proximity to the stream. This argues for the importance of both riparian settings for regulating catchment N dynamics.

Key words: nitrogen, groundwater, riparian, ecohydrology